Media communication system, and terminal apparatus and signal conversion apparatus in said system

ABSTRACT

Disclosed is a media communication system in which communication of media such as sound, image and the like is performed between first and second terminals, each of which is constructed so as to be capable of IP communication, via an IP network. The system includes an IP packetizing unit for IP-packetizing and sending, to the IP network, a media signal sent from the first terminal, and for converting an IP packet received from the IP network to a media signal and sending the media signal to the first terminal, and a media signal transmitting unit for connecting a media/signal converter, which is provided within the first terminal, to the IP packetizing unit to transmit a media signal.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a media communication system, aterminal apparatus and a signal conversion apparatus used in thissystem. In particularly, the invention relates to a media communicationsystem for communication of media such as voice and images via an IPnetwork between terminals constructed so as to be capable of IPcommunication, as well as to a terminal apparatus and signal conversionapparatus used in this system.

[0002] VoIP (Voice over IP) technology through which telephonecommunication is implemented by IP communication has been developed andhas reached the product phase in recent years. What characterizes VoIPtechnology is the fact that a voice signal is transmitted via IPcommunication. By using IP communication to control a terminal that hasbeen connected to an IP communication network, the provision of moreflexible services can be expected. In order to realize VoIPcommunication, a protocol stipulated by ITU-T Recommendation H.323 hasbeen developed and is now in wide use. In recent years, moreover,consideration has been given to controlling the connection of calls bySIP (Session Initiation Protocol). Study of this protocol is beingforwarded with a view to implementation.

[0003] In order to maintain the quality of voice when voice istransmitted using IP communication, variations in transmission delay ofthe IP packets that transport voice must be not be allowed to exceed acertain fixed value, and techniques for maintaining the networkconditions of IP communication for this purpose are being studiedwidely. Voice communication at a problem-free quality is feasible evenat the present time if the communication path for carrying out IPcommunication has a bandwidth sufficiently. If this is not the case,however, the state of the art is such that voice quality cannot bemaintained satisfactorily. Investigations and research in this area arebeing conducted aggressively at the present time.

[0004] In communication systems in which wireless communication is usedup to the terminal, as in cellular telephone systems, the data transferbandwidth over such wireless segments of the communication path is notlarge. As a consequence, if communication traffic by way of IP isincreased for the purpose of achieving more economical communication,the IP communication traffic in the wireless segments increases and sodoes delay. In an instances where IP communication is performed using anordinary telephone line, an increase in traffic will make it difficultto carry out high-quality voice communication unless sufficientbandwidth is provided for the IP network.

[0005] Thus, there is keen demand for a method or system that willassure voice quality by reducing delays in the transmission of voice IPpackets even when there is an increase in IP communication traffic.

[0006] The present invention seeks to solve the abovementioned problemby performing media communication such as voice communication throughconventional communication techniques without relying upon IPcommunication over segments of the transmission path where sufficientbandwidth cannot be acquired. As a result, control of a terminal can becarried out by IP communication while assuring the quality of voice, andit is possible to realize a media communication system that provides theflexible service that is the characterizing feature of VoIPcommunication. It should be noted that although the present invention isapplied to general media communication inclusive of voice communication,the invention will be described with regard to voice communicationbecause limiting the discussion to voice communication will betterfacilitate an understanding of the invention. However, since voicecommunication is but one form of media communication, it will readily beunderstood that the invention can be expanded to cover other mediacommunication. In other words, the present invention is not limited tovoice communication.

[0007]FIG. 16 is a block diagram showing the configuration of a networkfor implementing ordinary VoIP communication according to the prior art.Here a VoIP terminal 101 (VoIP terminal A) and a VoIP terminal 102 (VoIPterminal B) are connected to an IP network 130. The VoIP terminal 101has a control unit 120 for performing connection control and mediacontrol, a voice/signal converter 122 for performing a conversionbetween voice and an electric signal, and an IP packetizing unit 124having a function for placing a voice signal in an IP packet. The VoIPterminal 101 further includes an IP interface 126 for transmitting acontrol-signal IP packet sent and received under the control of thecontrol unit 120, and for receiving a control-signal IP packet from theIP network 130, and an IP interface 128 for transmitting a voice-signalIP packet to the IP network 130 and receiving a voice-signal IP packetfrom the IP network 130. The VoIP terminal 102 has a structure similarto that of the VoIP terminal 101.

[0008] A procedure for connecting the call of a VoIP terminal generallyis carried out in phases as shown in FIG. 17. The procedure, which isdescribed in Chapter 8 of ITU-T Recommendation H.323 stipulating theH.323 procedure, can be divided into five phases, namely Phase A, PhaseB, . . . , Phase E. Each phase will now be described with regard to acase where voice is communicated upon connecting terminals A and Btogether.

[0009] 1. Phase A: Call Setup Phase

[0010] This phase is a procedure through which agreement is obtained forthe purpose of setting up a call between the two terminals. If the VoIPterminal 101, which is the originating terminal, is operated by a userto issue a call, then the VoIP terminal 101 sends a Setup message, whichis for setting up the call, to the VoIP terminal 102, and the latterresponds to receipt of the Setup message by deciding whether or not toset up the call. If the call is set up, the VoIP terminal 102 notifiesthe VoIP terminal 101 of call set-up by a Connect message and reportsalso the address (connect address) that will be necessary in the ensuingPhase B. The details of the procedure of Phase A will now be describedwith reference to FIG. 18. The latter is an example that makes use ofthe H.323 protocol.

[0011] First, a connection controller 141 in the control unit 120 ofVoIP terminal 101 determines the destination using the IP address of anIP interface 127 of a control unit 121 in the VoIP terminal 102, editsan IP packet that contains a message (Set Up message 301) for requestingcall set-up and requests the IP interface 126 to transmit this IPpacket. The IP interface 126 transmits the IP packet to the IP interface127 of VoIP terminal 102. In this case, it is required that the controlunit 120 know the IP address of the VoIP terminal B. In order tosimplify the description, however, it will be assumed that the controlunit 120 already knows this IP address. A method of acquiring an IPaddress when the IP address is unknown is well known in the art and isdescribed also in the H.323 documentation.

[0012] Upon receiving the Set-Up message 301 from the VoIP terminal 101,the IP interface 127 of VoIP terminal 102 delivers this request messageto a connection controller 143 in the control unit 121. The connectioncontroller 143 determines whether a call can be connected in response tothe Set-Up message 301 and, if it determines that the call can beconnected, sends back an answer message (Connect message 302) to theVoIP terminal 101. The Connect message 302 reports the IP address andport number to be contacted by the VoIP terminal 101 in Phase B. In theexample of FIG. 16, the contact address is constituted by the IP addressand port number necessary to communicate with a media controller 144that exercises control in Phase B. Accordingly, the IP address of the IPinterface 127 and the port number for selecting the media controller 144are reported to the VoIP terminal 101 as the contact address. Uponreceiving the above-mentioned answer message, the VoIP terminal 101 ineffect agrees with the other terminal to connect the call and deliversthe privilege for subsequent control to a media controller 142 (Start303 in FIG. 18) together with the IP address and port number of the VoIPterminal 102 to be contacted.

[0013] 2. Phase B: Initial Communication and Capability Exchange

[0014] The media controller 142 of VoIP terminal 101 edits informationnecessary for voice communication, the information including (1) thevoice encoding scheme of the VoIP terminal 101, (2) the IP address ofthe IP interface 128 that sends and receives voice packets, and (3) theport number of the IP packetizing unit 124, and sends this information(Open Logical Channel message 304) to the destination indicated by theIP address and port number of the VoIP terminal 102 that were reportedthrough the procedure of Phase A. Upon receiving this message, the mediacontroller 144 of control unit 121 in VoIP terminal 102 determineswhether the voice encoding scheme on the side of VoIP terminal 102matches the requested encoding scheme. If the schemes match and voicecommunication is possible, the media controller 144 edits informationnecessary for voice communication, the information including the IPaddress of an IP interface 129 of VoIP terminal 102 that sends andreceives voice packets, and a port number for selecting a voice IPpacketizing unit 125, and sends this information to the VoIP terminal101 (Open Logical Channel Ack 306). As a result of these operations,information for communicating voice between the VoIP terminals 101, 102is obtained on both sides.

[0015] In a case where SIP (Session Initiation Protocol) is used to makethe connection instead of the H.323 protocol, the sequence becomes asshown in FIG. 19. In this case, Phases A and B are consolidated andexpressed by a single message. Specifically, the connection controller141 of VoIP terminal 101 queries the media controller 142 regarding theconditions usable in media communication (401) and, as a result,information necessary for media communication, namely the voice encodingscheme of the VoIP terminal 101, the IP address of the IP packetizingunit 124 and the port number, etc., is obtained. The connectioncontroller 141 sends the call set-up request, which is inclusive of thisinformation, to the connection controller 143 of VoIP terminal 102(Invite message 402). Upon receiving the Invite message 402, the VoIPterminal 102 determines whether the connection can be established and,if the connection can be established, reports the conditions of VoIPterminal 101 to the media controller 144 of VoIP terminal 102, acquiresthe conditions (403) on the side of VoIP terminal 102 from the mediacontroller 144 and sends this information to the VoIP terminal 101 by anOK message (404). In order to verify receipt of the OK message, the VoIPterminal 101 transmits an ACK message to the VoIP terminal 102 (416).

[0016] The connection controller 141 of VoIP terminal 101 delivers theinformation of the OK message to the media controller 142. As a resultof these operations, information for communicating media between theVoIP terminals 101, 102 is obtained on both sides.

[0017] 3. Phase C: Establishment of Audiovisual Communication

[0018] The media controllers 142, 144 of the control units in both VoIPterminals notify the IP packetizing units 124, 125 of the destination IPaddresses and port numbers, which are for sending and receiving voicepackets, acquired through the above-described procedure, and the IPpacketizing units 124, 125 start sending the voice signal using thereported IP addresses and port numbers as the destinations. Startmessages 305, 307 in FIG. 18 and Start messages 407, 408 in FIG. 19correspond to the parts of the procedure set forth above.

[0019] The voice packet arrives at the IP interface 129 having the setIP address of the destination and the packet is input to thereceiving-side IP packetizing unit 125 selected by the specified portnumber. Next, the IP packetizing unit 125 converts the IP packet to avoice signal and a voice/signal converter 123 converts the voice signalto voice and outputs the same. The voice signal in the oppositedirection is transmitted in a similar manner, whereby voicecommunication becomes possible (308 in FIG. 18 and 409 in FIG. 19).

[0020] 4. Phase D: Call Service

[0021] By changing the IP address of the communicating party to anotherIP address during a call, it is possible with the communicationestablished in Phase C to change the destination of the connection.Services such as third-party conversion and call transfer areimplemented using this function.

[0022] 5. Phase E: Call Termination

[0023] In order to release a connected call, the connection controller141 on the calling side sends a release request message (Release message309 in FIG. 18 and Bye message 410 in FIG. 19) to the VoIP terminal 102on the called side and instructs the IP packetizing unit 124 toterminate the sending of voice (313, 314 in FIG. 18 and 414, 415 in FIG.19). Upon receiving the release request message, the connectioncontroller 143 of the VoIP terminal 102 instructs the IP packetizingunit 125 to halt the sending of voice (311, 312 in FIG. 18 and 412, 413in FIG. 19) and sends a message to answer the release request (ReleaseAck 310 in FIG. 18 and OK 411 in FIG. 19). As a result, the resourcesthat were being used in the connection of the call are released and thecall can be disconnected.

[0024] If the VoIP terminal 101 that requested release cannot receiveRelease Ack 310 within a fixed period of time, this terminal resends therelease request message. This makes it possible to release the callconnection reliably even in cases where the message has been lost.

[0025]FIG. 20 is a diagram showing the network configuration of aconventional All-IP architecture inclusive of a wireless transmissionsegment. Here a mobile network inclusive of a wireless segment isconstructed by a cellular telephone terminal 51, which is a mobilestation, a wireless base station 52, an SGSN (Serving GPRS Support Node)53 and a GGSN (Gateway GPRS Support Node) 54. GPRS (General Packet RadioService) is a function having 3GPP architecture that provides the mobilesubscriber with a packet-data service. SGSN 53 and GGSN 54 are bothnodes having a gateway function for a 3GPP core network furnished with apacket service. SGSN 53 is provided on the side of the base station,GGSN 54 is provided on the side of an IP network 55 and both send andreceive packets in accordance with the GTP protocol.

[0026] Connected to the IP network 55 in addition to the GGSN 54 are anSIP proxy server 56, which performs connection control, and an IPtelephone (IP Tel) 57. Furthermore, a PSTN (Public Switched TelephoneNetwork) 59 is connected to the IP network 55 via a media gateway (MG)58.

[0027] In response to a request from a user to originate a call, thecellular telephone terminal 51 creates an IP packet inclusive of aninvite message in accordance with SIP/TCP/IP and sends the packet to theSIP proxy server 56 via the wireless base station 52, SGSN 53, GGSN 54and IP network 55 in the order mentioned. The SIP proxy server 56obtains the IP address of the communication destination based uponinformation concerning the communicating party contained in the invitemessage and sends the invite message to this communication destination.If connection to the cellular telephone terminal 51 is possible, thecommunication destination sends the IP packet, which includes an OKmessage, to the cellular telephone terminal 51 by way of the SIP proxyserver 56. The cellular telephone terminal 51 thenceforth places voicein an IP packet in accordance with RTP/UDP/IP and transmits this IPpacket to the communicating party via the wireless base station 52, SGSN53, GGSN 54 and IP network 55 in the order mentioned. The voice packetfrom the communicating party is received, returned to a voice signal andoutput. It should be noted that RTP stands for Real-time TransportProtocol.

[0028] Thus, in conventional VoIP communication, the VoIP terminal isconnected to the server (the SIP proxy server in FIG. 20) and controlsignals are exchanged by the server and terminal to effect theconnection between them. In this case, the server need only be connectedto the IP network and therefore connection control can be carried oututilizing any server that does not depend upon a telephone company. Thisis advantageous in that flexible service can be provided.

[0029] In summation, the following advantages (1) to (3) are obtained inaccordance with VoIP communication of the conventional All-IParchitecture:

[0030] (1) End-to-end control is possible. Service can be implemented bythe functionality of a terminal or by the functionality of a node(server) that is independent of a network.

[0031] (2) Because end-to-end control can be carried out, a mechanismfor service implementation can be constructed independently of an IPnetwork. Further, functions for implementing service can be utilized incommon by various communication networks and, hence, the cost of serviceimplementation can be reduced.

[0032] (3) If IP data communication increases, so does data traffic anda strategy is instituted to increase the capacity of the IP network tocope with this. If the capacity of the IP network is enlarged, theamount of communication resources for special communication such asvoice communication declines in comparison with the capacity possessedby the IP network and it becomes unnecessary to set aside resources.

[0033] Nevertheless, VoIP communication of the conventional All-IParchitecture has certain problems, which are as follows:

[0034] (1) Human beings are sensitive to voice quality. It is necessary,therefore, to provide a high IP-communication quality in order to avoida decline in voice quality as caused by delay of IP packets. With theprior art, however, measures for dealing with delay of IP packets areunsatisfactory and high-quality communication of voice cannot beachieved. A decline in quality due to delay is great especially whenthere is a segment in the communication path that does not possesssufficient bandwidth for data transmission.

[0035] (2) An IP packet is composed of a header and payload, andoverhead resulting from the header is large. The problem that arises isthat efficient communication cannot be carried out in the case of voicecommunication where the amount of data in one IP packet is small. Morespecifically, with voice communication, it is necessary to send IPpackets in short intervals (e.g., 20 ms) and therefore sophisticatedfunctionality is needed to compress the header. This is not easy tofurnish.

[0036] (3) In instances where radio communication is used, as in thecase of a cellular telephone, the data transmission bandwidth over thewireless segment of the transmission path is small. Delay over such asegment is large and degrades voice quality. In networks that havewireless segments, therefore, sophisticated techniques are required toimplement IP communication with high quality. This is not easy.

[0037] (4) In order to raise the voice quality of a cellular telephone,the signal is transmitted upon being separated into a portion that isimportant for voice and a portion of lesser importance. If the samemethod is employed with communication of IP packets, however, the amountof data contained in one IP packet diminishes even further and efficienttransmission is difficult to accomplish.

[0038] (5) As mentioned above, it is necessary to send IP packets atsmall intervals (e.g., 20 ms) in order to transmit voice using IPpackets. As a consequence, the number of IP packets sent over a fixedperiod of time is large and the routers that transfer the IP packetsrequire a high processing capability. In particular, when a firewall isused to maintain security, processing for verifying all voice IP packetsis required. The result is an increase in amount of processing, making ahigh-performance firewall necessary. This raises cost.

[0039] (6) Though VoIP devices have proliferated, conventional voicetelephone equipment is still prevalent by far. This means that it isnecessary to utilize conventional voice telephone facilitiesefficiently. However, such facilities cannot be exploited satisfactorilywith the conventional All-IP architecture.

SUMMARY OF THE INVENTION

[0040] Accordingly, an object of the present invention is to avoid adecline in voice quality as caused by delay of IP packets.

[0041] Another object of the present invention is to avoid a decline invoice quality even in a case where a transmission path includes asegment, e.g., a wireless segment, that does not have a sufficient datatransmission bandwidth.

[0042] Another object of the present invention is to prevent a declinein voice quality and make it possible to provide flexible service.

[0043] A further object of the present invention is to make it possibleto set up calls and provide service through handling that is entirelythe same as that of a conventional VoIP terminal.

[0044] A further object of the present invention is to dispense with ahighly sophisticated function for compressing headers for the purpose ofimproving upon the overhead of headers.

[0045] Yet another object of the present invention is to dispense withprocessing for verifying voice IP packets in a firewall.

[0046] Another object of the present invention is to utilizeconventional voice communication equipments effectively.

[0047] According to a first aspect of the present invention, there isprovided a media communication system for performing media communicationbetween first and second terminals, each of which is constructed so asto be capable of IP communication, via an IP network, the systemcomprising: (1) an IP packetizing unit for IP-packetizing and sending,to the IP network, a media signal sent from the first terminal, and forconverting an IP packet received from the IP network to a media signaland sending the media signal to the first terminal, and (2) a mediasignal transmitting unit for connecting a media/signal converter, whichis provided within the first terminal, to the IP packetizing unit, andfor transmitting a media signal. The first terminal has, in addition tothe media/signal converter for generating a media signal and receiving amedia signal from the IP packetizing unit, a controller for controllingconnection to the second terminal and for controlling sending/receivingof a media signal. When a call is generated, the controller (1) performscontrol in such a manner that the IP packetizing unit operates as itsown IP packetizing unit and (2) controls the media signal transmittingunit to connect the media/signal converter and the IP packetizing unitso as to make transmission of a media signal possible. Upon completionof the connection control, the controller (3) sends and receives mediasignals to and from the second terminal via the media/signal converter,the media signal transmitting unit, the IP packetizing unit and the IPnetwork.

[0048] In accordance with the first aspect of the present invention, theIP-packetization of voice takes place not in the terminal but in the IPpacketizing unit disposed in close proximity to the IP network. As aresult, VoIP communication with little degradation of voice quality ispossible. Moreover, it is possible to carry out end-to-end control,which is one of the merits of VoIP communication, thereby enabling theprovision of flexible service.

[0049] Further, in accordance with the first aspect of the presentinvention, even if there is a segment of the communication path thatdoes not have sufficient data transmission bandwidth, e.g., a wirelesssegment, voice is transmitted over this segment as it is without beingconverted to a voice IP packet. As a result, delay of IP packets can bereduced and a decline in voice quality can be avoided. In addition,since delay of IP packets can be reduced, the size of overhead in theheader of an IP packet does not present a problem and it is possible todispense with a highly sophisticated header compression function.

[0050] Further, in accordance with the first aspect of the presentinvention, voice is transmitted as it is using a public network ormobile network without relying upon IP packetizing over segments that donot possess sufficient data transmission bandwidth. As a result,conventional voice telephone equipment can be utilized effectively.

[0051] Further, since a terminal in the present invention can beprovided with an interface exactly the same as that of the conventionalVoIP terminal, it is possible to set up calls and provide servicethrough handling that is exactly the same as that of the usual VoIPterminal.

[0052] According to a second aspect of the present invention, there isprovided a media communication system for performing media communicationbetween first and second terminals, each of which is constructed so asto be capable of IP communication, via an IP network, the systemcomprising: (1) a public IP network to which the first terminal isconnected; (2) a private VoIP network (intracorporate IP network) towhich the second terminal is connected and which is capable of IP mediacommunication by an extension; (3) a firewall provided between thepublic IP network and the intracorporate IP network; (4) an IPpacketizing unit for IP-packetizing and sending, to the intracorporateIP network, a media signal sent from the first terminal, and forconverting an IP packet received from the intracorporate IP network to amedia signal and sending the media signal to the first terminal; and (5)a media signal transmitting unit for connecting a media/signalconverter, which is provided within the first terminal, to the IPpacketizing unit, and for transmitting a media signal.

[0053] The first terminal has, in addition to the media/signal converterfor generating a media signal and receiving a media signal from the IPpacking unit, a controller for controlling connection to the secondterminal and for controlling sending/receiving of a media signal. When acall is generated, the controller (1) performs control in such a mannerthat the IP packetizing unit operates as its own IP packetizing unit and(2) controls the media signal transmitting unit to connect themedia/signal converter and the IP packetizing unit so as to maketransmission of a media signal possible. Upon completion of theconnection control, the controller (3) sends and receives media signalsto and from the second terminal via the media/signal converter, themedia signal transmitting unit, the IP packetizing unit and theintracorporate IP network.

[0054] In accordance with the second aspect of the present invention, itis possible for an enterprise having a VoIP-based extension tocommunicate just as if a connection has been made to the extension fromthe outside using an existing telephone network. This makes possible theimplementation of highly effective means for use as intracorporatecommunication means.

[0055] According to a third aspect of the present invention, there isprovided a media communication system for performing media communicationbetween first and second terminals, each of which is constructed so asto be capable of IP communication, via an IP network, the systemcomprising: (1) an intracorporate, closed internal IP network (such asintracorporate IP network) to which the first terminal is connected andwhich is capable of IP media communication; (2) a public IP network towhich the second terminal is connected; (3) a firewall provided betweenthe intracorporate IP network and the external IP network (public IPnetwork); and (4) IP-packet relay means provided between theintracorporate IP network and public IP network for relaying only IPpackets of a media signal that bypasses the firewall. The first terminalhas an IP packetizing unit for IP-packetizing a media signal and sendingit to the internal IP network, and for converting an IP packet receivedfrom the internal network to a media signal; and a controller forcontrolling connection to the second terminal and for controllingsending/receiving of a media signal when a call is generated. When acall is generated, the controller (1) performs control via theintracorporate IP network, firewall and public IP network in such amanner that the IP-packet relay means operates as its own relay meansand (2) controls connection via the intracorporate IP network, IP-packetrelay means and public IP network in such a manner that a media signalis capable of being transmitted. Upon completion of connection control,the controller (3) sends and receives media signals to and from thesecond terminal via the intracorporate IP network, IP-packet relay meansand public IP network.

[0056] In accordance with the third aspect of the present invention, itis possible to dispense with processing for verifying voice IP packetsat the firewall. This makes it possible to reduce the amount of firewallprocessing, to dispense with the need to provide the firewall withsophisticated functionality and to hold down cost.

[0057] According to a fourth aspect of the present invention, there isprovided a signal conversion apparatus provided in a radio base-stationfacility and connected to an asynchronous communication network (e.g.,an IP network) which is controled by the terminal using the controlsignals sent from the terminal. The signal conversion apparatuscomprises: (1) first conversion means for converting a synchronous voicesignal, which the base station has received from a mobile station via aradio channel, to an asynchronous voice signal directed to a destinationthat has been set; (2) first sending means for sending the asynchronousvoice signal obtained by the conversion to the asynchronouscommunication network; (3) second conversion means for receiving anasynchronous voice signal from the set destination via the asynchronouscommunication network and converting this signal to a synchronous voicesignal; and (4) second sending means for sending the synchronous voicesignal obtained by the conversion to the radio base station in such amanner that this signal will be transmitted to the mobile station viathe radio channel.

[0058] According to a fifth aspect of the present invention, there isprovided a terminal apparatus in a media communication system forsending and receiving media signals between terminals via an IPpacketizing unit for IP-packetizing a media signal and sending it to anIP network and for converting an IP packet received from the IP networkto a media signal, a media signal transmitting unit for transmitting amedia signal between a terminal and the IP packetizing unit, and the IPnetwork, the terminal apparatus comprising: (1) a media/signal converterfor generating and sending a media signal and receiving a media signalfrom the IP packetizing unit via the media signal transmitting unit, and(2) a controller which, when a call is generated, is for performingcontrol in such a manner that the IP packetizing unit operates as itsown IP packetizing unit and for controlling the media signaltransmitting unit to connect the media/signal converter and the IPpacketizing unit.

[0059] In accordance with the fourth and fifth aspects of the presentinvention, it is possible to provide a terminal apparatus and a signalconversion apparatus that can be used in the first to third aspects ofthe present invention.

[0060] Other features and advantages of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0061]FIG. 1 is a block diagram showing the construction of a firstembodiment of the present invention;

[0062]FIG. 2 is a block diagram showing an example of implementation (anexample using a telephone network) of voice signal transmitting meansaccording to the first embodiment;

[0063]FIG. 3 is a diagram useful in describing a procedure forconnecting a VoIP call;

[0064]FIG. 4 shows a VoIP call connection sequence (in case of H.323)when a call is originated;

[0065]FIG. 5 shows a sequence for connecting a voice/signal converterand an IP packetizing unit;

[0066]FIG. 6 shows a VoIP call connection sequence (in case of SIP) whena call is originated;

[0067]FIG. 7 shows a VoIP call connection sequence (in case of H.323) atthe time of an incoming call;

[0068]FIG. 8 shows a VoIP call connection sequence (in case of SIP) atthe time of an incoming call;

[0069]FIG. 9 is a block diagram showing an example of implementation ofvoice signal transmitting means according to a second embodiment;

[0070]FIG. 10 shows a VoIP call connection procedure for a case where anIP packetizing unit (media gateway) is disposed within a public network;

[0071]FIG. 11 shows a sequence for connecting a voice/signal converterand a media gateway;

[0072]FIG. 12 is a block diagram illustrating a modification of thesecond embodiment;

[0073]FIG. 13A is a block diagram showing the construction of a thirdembodiment of the present invention;

[0074]FIG. 13B is a partial block diagram of a signal conversionapparatus;

[0075]FIG. 13C is a block diagram illustrating a modification of thethird embodiment;

[0076]FIG. 14 is a block diagram illustrating a fourth embodiment of thepresent invention;

[0077]FIG. 15 is a block diagram illustrating a fifth embodiment of thepresent invention;

[0078]FIG. 16 is a block diagram illustrating ordinary VoIP according tothe prior art;

[0079]FIG. 17 is a diagram useful in describing a procedure forconnecting VoIP calls according to the prior art;

[0080]FIG. 18 shows a VoIP call connection sequence (in case of H.323)according to the prior art;

[0081]FIG. 19 shows a VoIP call connection sequence (in case of SIP)according to the prior art; and

[0082]FIG. 20 is a diagram showing All-IP architecture according to theprior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] (A) Overview of the invention

[0084] Media Communication According to the Invention

[0085]FIG. 1 is a block diagram showing the configuration of a mediacommunication system according to a first embodiment of the presentinvention. Media communication (e.g., voice communication) is carriedout via an IP network 130 between a terminal 103 (terminal A) and aterminal 102 (terminal B) each of which is capable of performing IPcommunication. The media communication system includes: an IPpacketizing unit 150 for IP-packetizing and sending, to the IP network130, a voice signal sent from terminal A, and for converting an IPpacket received from the IP network 130 to a voice signal and sendingthe voice signal to terminal A, and a voice signal transmitting unit 160for connecting a voice/signal converter 122, which is provided withinterminal A, to the IP packetizing unit 150, and for sending voicesignals. The terminal A has, in addition to the voice/signal converter122, a control unit 120 for controlling connection to the other terminal102 and for controlling sending/receiving of voice signals when a callis generated.

[0086] When a call is generated, terminal A performs control in such amanner that the IP packetizing unit 150 operates as its own IPpacketizing unit and controls the voice signal transmitting unit 160 toconnect the voice/signal converter 122 and the IP packetizing unit 150so as to make transmission of a voice signal possible. Upon completionof the connection, the terminal A sends and receives voice signals toand from terminal B, which is the destination of communication, via thevoice/signal converter 122, the voice signal transmitting unit 160, theIP packetizing unit 150, an IP interface 151 and the IP network 130.

[0087] More specifically, when the control unit 120 performs connectioncontrol, the controller (1) communicates with the IP packetizing unit150 via the IP interface 126 and IP network 130 to acquire the IPaddress and port number of the IP packetizing unit 150, (2) reports thisIP address and port number to terminal B at the destination via the IPnetwork 130, and (3) receives the IP address and port number of terminalB from terminal B and reports these to the IP packetizing unit 150. (4)The IP packetizing unit 150 receives and packetizes a voice signal fromthe voice/signal converter 122 via the voice signal transmitting unit160 and sends the resulting packet to the IP network 130 using the IPaddress and port number of terminal B as the destination. (5) Meanwhile,terminal B at the destination sends a voice-signal IP packet to the IPnetwork 130 using the IP address and port number of the IP packetizingunit 150 as the destination, and (6) the IP packetizing unit 150restores the IP packet received from the IP network to a voice signaland sends the voice signal to the voice/signal converter 122 via thevoice signal transmitting unit 160, whereby the voice signal is outputas voice from a speaker or the like, not shown.

[0088] If the above-described arrangement is adopted, theIP-packetization of voice is performed not in the terminal 103 but inthe IP packetizing unit 150 (signal conversion apparatus 155) disposedin close proximity to the IP network 130. As a result, VoIPcommunication with little degradation of voice quality is possible.Moreover, it is possible to carry out end-to-end control, which is oneof the merits of VoIP communication, thereby enabling the provision offlexible service.

[0089] Voice Signal Transmitting Unit 160

[0090] The voice signal transmitting unit 160 is implemented by a publictelephone, as shown by way of example in FIG. 2. To accomplish this,telephones 162, 163 and telephone controllers 165, 166 are provided onthe side of terminal A and on the side of the IP packetizing unit 150and the control unit 120 of terminal A controls these telephonecontrollers to connect the voice/signal converter 122 and IP packetizingunit 150 in such a manner that voice signals can be transmitted betweenthem.

[0091] In this case, the voice signal transmitting unit 160 can beimplemented using a mobile communication network as the public telephonenetwork, as illustrated in FIG. 13A. Since a mobile communicationnetwork is capable of communication with includes the communication ofdata, the communication means between terminal A and the IP network canbe implemented using this mobile communication network. As a result,when a mobile communication network is employed, it is possible for thetransmission of IP packets and the transmission of media (voice, images,etc.) to be achieved using the same mobile communication network. Thismakes it possible to realize more efficient communication.

[0092] If voice is transmitted by the voice signal transmitting unit 160using a public telephone network, the connection between thevoice/signal converter 122 and the IP packetizing unit 150 isimplemented by an outgoing call from the side of the IP packetizing unit150, thereby achieving the voice transmission. If this arrangement isadopted, the above-mentioned connection using a selected prescribedtelephone can readily be achieved even if a plurality of telephones areconnected to the IP packetizing unit 150. A further advantage is thatthis can be performed automatically.

[0093] Further, if voice is transmitted by the voice signal transmittingunit 160 using a public telephone network, the connection between thevoice/signal converter 122 and the IP packetizing unit 150 isimplemented by an outgoing call from the telephone 163 (FIG. 2) on theterminal side, thereby achieving the voice transmission. If thisarrangement is adopted, the telephone number of the telephone 162 on theside of the IP packetizing unit 150 is allowed to be acquired by theterminal 103 in advance, as a result of which the abovementionedconnection can be made automatically by making transmission to thistelephone number. Further, the charge to the originating terminal A forvoice transmission over the public telephone network can readily bebilled using the billing function of the public telephone network.

[0094] IP Packetizing Unit 150

[0095] The IP packetizing unit 150 is placed within the pubic networkand the connection for transmitting voice between the terminal 103 andthe IP packetizing unit 150 is made using the functionality of thepublic network. A media gateway (MG) 171 disposed in the public networkin the manner shown in FIG. 9 is used as the IP packetizing unit 150,and the voice connection between the media gateway MG and voice/signalconverter 122 of terminal A is implemented using a switch 170 in thepublic network. The media gateway MG is controlled by a media gatewaycontroller (MGC) 712 in accordance with a predetermined protocol. Inorder for the terminal 103 to control the media gateway MG as the IPpacketizing unit, therefore, this is implemented via the media gatewaycontroller MGC.

[0096] The media gateway controller MGC and the switch 170 are connectedby an ordinary public-network signaling system, e.g., Common ChannelSignaling System No. 7. Control for connecting voice calls can becarried out by such signaling. Though a scheme for implementing VoIPcommunication that uses the media gateway MG and media gatewaycontroller MGC is known, the scheme of the present invention differs inthat the connection from the media gateway MG to terminal B isimplemented by having terminal A communicate directly with terminal B orwith a server (e.g., an SIP proxy server) that performs VoIP voicecontrol. With the conventional scheme, basically the control of aconnection from the media gateway MG to terminal B is performed by themedia gateway controller MGC.

[0097] In a case where voice is transmitted via the voice signaltransmitting unit 160 constituted by the public telephone network, theconnection between the voice/signal converter 122 and media gateway 171is implemented by a call that originates from the media gatewaycontroller 172, thereby allowing voice transmission to take place.Generally speaking, the media gateway MG is connected to the switch 170via a plurality of lines. Even this case an advantage is that aprescribed line can be selected and readily connected by placing a callfrom the media gateway controller MGC.

[0098] Further, in a case where voice is transmitted via the voicesignal transmitting unit 160 constituted by the public telephonenetwork, the connection between the voice/signal converter 122 and mediagateway 171 is implemented by a call that originates from the telephone163 on the terminal side. In order to effect the connection to thepertinent line of the media gateway MG in this case, the media gatewaycontroller MGC previously assigns a number to each line and notifies theterminal 103 of the numerals to be dialed, inclusive of the assignednumber. The applicable line is selected by this number. If thisarrangement is adopted, the charge for voice transmission over thepublic telephone network can readily be billed on the side of theoriginating terminal using the functionality of the public telephonenetwork.

[0099] Virtual MGC

[0100] As shown in FIG. 12, the control unit 120 of terminal A isprovided with a control function similar to that of the media gatewaycontroller (MGC) 172, and the elements from the telephone 163 on theside of terminal A to the media gateway (MG) 171 are regarded as onevirtual media gateway 200. If this arrangement is adopted, terminal Acan control the virtual media gateway 200 utilizing a protocol (Megacoprotocol) the same as that which the media gateway controller MGC usesto control the media gateway MG. By virtue of this arrangement, aprotocol for controlling the media gateway controller MGC from terminalA need not be defined anew; the connection of the voice signaltransmitting unit can be set up utilizing the already defined Megacoprotocol.

[0101] Utilization of Mobile Communication Network

[0102] The voice signal transmitting unit 160 can be implemented by amobile communication network in the manner shown in FIG. 13A. Because aterminal (A) 104 and a radio base station 181 are connected wirelesslyin an mobile communication network, the IP packetizing unit 150 isplaced in the radio base station or in the base-station control office.Further, since the mobile terminal and the radio base station orbase-station control office exchange control signals to connect a callin a mobile communication network, the communication of control signalsbetween the terminal (A) 104 and IP packetizing unit 150 can beperformed using means the same as those which effect the exchange ofcontrol signals.

[0103] Further, if the voice signal transmitting unit 160 is implementedby a mobile communication network, then, in a manner similar to thatwhere the voice signal transmitting unit 160 is implemented by thepublic telephone network, the media gateway (MG) 171 is placed in themanual transmission as the IP packetizing unit 150, the terminal (A) 104and the media gateway (MG) 171 are connected via the radio base stationor base-station control office, and control of the media gateway MG canbe carried out by the media gateway controller (MGC) 172.

[0104] If the terminal A is implemented by a mobile communicationterminal, the terminal A is provided with the control function of themedia gateway controller MG and the elements from the voice/signalconverter 122 of terminal A to the media gateway MG placed in thenetwork are regarded as one virtual media gateway. If this arrangementis adopted, mobile terminal can control the virtual media gatewayutilizing a protocol (the Megaco protocol) the same as that which themedia gateway controller MGC uses to control the media gateway MG.

[0105] Arrangement for Connecting to Communication-destination TerminalVia Private VoIP (Intracorporate IP Network)

[0106] If a network (private VoIP network) 190 that is capable of IPmedia communication over a closed extension is present within acorporation or business, as shown in FIG. 14, it is necessary to adoptan arrangement in which media is communicated from the external terminal103 to the internal terminal 102 via the private VoIP network(intracorporate IP network). To this end, the media communication systemis provided with: (1) the public IP network 130 to which the externalterminal (first terminal) 103 is connected; (2) the intracorporate IPnetwork 190 to which the internal terminal (second terminal) 102 isconnected; (3) a firewall 191 provided between the intracorporate IPnetwork and the public IP network; (4) the IP packetizing unit 150 forIP-packetizing a voice signal sent from the first terminal and sendingit to the intracorporate IP network, and for converting an IP packetreceived from the intracorporate IP network to a voice signal; and (5)the voice signal transmitting unit 160 for connecting the voice/signalconverter 122, which is provided in the first terminal, to the IPpacketizing unit 150 to thereby transmit a voice signal.

[0107] The first terminal 103 (1) performs control via the IP network130, firewall 191 and intracorporate IP network 190 in such a mannerthat the IP packetizing unit 150 operates as its own IP packetizing unitwhen a call is generated, and (2) controls the voice signal transmittingunit 160 in such a manner that the internal voice/signal converter 122and IP packetizing unit 150 are connected. (3) Upon completion ofconnection control, the first terminal 103 sends and receives voicesignals to and from the second terminal 102 via the voice/signalconverter 122, voice signal transmitting unit 160, IP packetizing unit150 and intracorporate IP network 190. As a result, the first terminal103 can send voice signals using the intracorporate IP network 190 justas if it were connected directly to the intracorporate IP network 190,without the intervention of the firewall 191. In this case, the voicesignal transmitting unit can be implemented by a public telephonenetwork and mobile communication network.

[0108] Arrangement for Bypassing Firewall

[0109] The amount of processing associated with a firewall can bereduced by so arranging that voice IP packets will not traverse thefirewall. To this end, the media communication system includes thefollowing, as shown in FIG. 15: (1) an intracorporate, closed internalIP network (intracorporate IP network) 196 to which the first terminal101 is connected and which is capable of IP media communication; (2) theexternal IP network (public IP network) 130 to which the second terminal102 is connected; (3) a firewall 195 provided between the intracorporateIP network 196 and the public IP network 130; and (4) IP-packet relaymeans 197 provided between the intracorporate IP network 196 and publicIP network 130 for bypassing the firewall 195. The first terminal 101performs control via the intracorporate IP network 196, firewall 195 andIP network 130 in such a manner that, when a call is generated, theIP-packet relay means 197 operates as its own IP-packet relay means, and(2) controls connection in such a manner that a media signal is capableof being transmitted via the intracorporate IP network 196, IP-packetrelay means 197 and public IP network 130. (3) Upon completion of theconnection, the first terminal 101 sends and receives media signals toand from the second terminal 102 via the intracorporate IP network 196,IP-packet relay means 197 and public IP network 130.

[0110] (B) First Embodiment

[0111] (a) Overall Construction

[0112]FIG. 1 is a block diagram illustrating the overall construction ofa first embodiment of the present invention. Here the terminal 103(terminal A) and the VoIP terminal 102 (terminal B) are constructed soas to be capable of IP communication. Communication of madia isperformed between the two terminals via the IP network 130. The terminal103 includes the control unit 120 for performing connection control andmedia control, the IP interface 126 which allows the control unit 120 totransmit control signals via the IP interface 126, and the voice/signalconverter 122 for performing the conversion between voice and anelectric signal. The VoIP terminal 102 includes the controller 121 forperforming connection control and media control, the voice/signalconverter 123 for performing the conversion between voice and anelectric signal, the IP packetizing unit 125 which functions to placevoice signals in IP packets, and the IP interfaces 127, 129. The controlunit 120 of terminal A has the connection controller 141 for performingconnection control and the media controller 142 for performing mediacontrol, and the controller 121 of terminal B has the connectioncontroller 143 for performing connection control and the mediacontroller 144 for performing media control.

[0113] The IP packetizing unit 150 of the signal conversion apparatus155, which is provided externally of the terminal 103, IP-packetizes avoice signal, which is sent from the terminal 103, and sends the IPpacket in the direction of the terminal 102 via the IP interface 151 andIP network 130. The IP packetizing unit 150 further converts an IPpacket received from the IP network 130 to a voice signal and sends thevoice signal in the direction of the terminal 103. The voice signaltransmitting unit 160 connects the voice/signal converter 122, which isprovided within terminal 103, to the IP packetizing unit 150, and sendsvoice signals in both directions.

[0114] (b) Construction of Voice Signal Transmitting Unit 160

[0115]FIG. 2 is a block diagram showing an example of implementation ofthe voice signal transmitting unit 160 of FIG. 1. This is for a casewhere the voice signal transmitting unit 160 is implemented by a publictelephone network. The voice signal transmitting unit 160 includes apublic telephone network 161; the telephone 162 on the side of the IPpacketizing unit 150 and the telephone 163 on the side of terminal 103,both of which are connected to the public telephone network 161;telephone controllers 164, 165 for controlling the telephones 162, 163,respectively; and an IP interface 166 for connecting the telephonecontroller 164 to the IP network 130. The telephone 162 is providedbetween the public telephone network 161 and the IP packetizing unit150, and the telephone 163 is provided between the voice/signalconverter 122 and the public telephone network 161.

[0116] The media controller 142 of control unit 120 in terminal 103 isconnected directly to the telephone controller 165. The latter iscapable of controlling the telephone 163. The voice/signal converter 122is connected to the telephone 163 and is so adapted as to be capable ofsending and receiving voice signals to and from the IP packetizing unit150 via the public telephone network 161 and telephone 162. A voicesignal is the result of converting the voice of the user to an electricsignal. As mentioned above, voice signals can be sent to and receivedfrom a communicating party through the ordinary telephones 162, 163 andpublic telephone network 161. In the case of other media signals such asimage signals, signals in the voice band are transmitted upon beingmodulated, whereby these can be transmitted through the telephones andpublic telephone network.

[0117] The telephone controller 164 controls the telephone 162 connectedto the IP packetizing unit 150. The telephone controller 164 isconnected to the IP network 130 by the IP interface 166 and is capableof sending and receiving control signals to and from the mediacontroller 142 of terminal 103 via the IP network 130. The IPpacketizing unit 150 is connected to the IP network 130 via the IPinterface 151. As a result of these connections, the media controller142 of terminal A is capable of controlling the IP packetizing unit 150by sending and receiving control signals to and from the IP packetizingunit 150 via the IP network 130.

[0118] (c) Connection Sequence

[0119] As shown in FIG. 3, the VoIP connection sequence of the presentinvention has an additional phase S as compared with the conventionalVoIP connection sequence (see FIG. 17). In Phase S, the voice signaltransmitting unit 160 is controlled to connect the voice/signalconverter 122 of terminal 103 with the IP packetizing unit 150. It isnot necessary to execute this phase for each individual call; the phasecan be used jointly by multiple calls. In other words, once thevoice/signal converter 122 of the originating terminal A and the IPpacketizing unit 150 have been connected in the phase, a plurality ofcalls can be connected using this connection.

[0120] 1. Phase S: Media Connection Setup

[0121] Phase S is a phase that precedes the connection of a call. Asmentioned above, this phase controls the voice signal transmitting unit160 to connect the voice/signal converter 122 of terminal 103 and the IPpacketizing unit 150 and makes it possible to IP-packetize a voicesignal by the IP packetizing unit 150. After the procedure of Phase S iscompleted, the connection sequence is identical with that of ordinaryVoIP communication shown in FIG. 18 and a call can be set up through asimilar procedure. It is possible to set up multiple calls as well.

[0122]FIG. 4 is a diagram useful in describing the connection sequenceof a VoIP call when the call is originated. FIG. 4 employs the H.323protocol. If the user performs an operation to originate a call, theconnection controller 141 of terminal 103 orders the media controller142 to prepare for media communication (i.e., sends a Preparationmessage 330) before the connection is established. Upon receiving thePreparation message 330, the media controller 142 sends a Requestmessage 331 to the IP packetizing unit 150 to request resources forconverting voice to an IP packet. In response to this request, the IPpacketizing unit 150 sends back, by way of a Response message 332, thenecessary information such as the IP address and port number of thepacketizing unit that performs the IP packetizing, and the encodingscheme used when the voice signal is IP-packetized. The IP packetizingunit 150 reports both the IP address and port number of the telephonecontroller 164 of its own connected telephone 162.

[0123] Next, the media controller 142 sends a Connect Request message341 to the voice signal transmitting unit 160 via the IP network 130 toconnect the voice/signal converter 122 of terminal 103 and the IPpacketizing unit 150, and the telephone controller 164 sends a ConnectComplete message to the media controller 142 at completion of theconnection.

[0124] This will be described in greater detail with reference to FIG.5. The media controller 142 reports the telephone number of telephone163 connected to the voice/signal converter 122 to the telephonecontroller 164 having the IP address and port number acquired throughthe above-described procedure and requests origination of a call to thistelephone number via the IP network (Connect Request 441 in FIG. 5).Further, the media controller 142 requests the telephone controller 165of telephone 163 on the side of the voice/signal converter 122 to answerif there is an incoming call (answer preparation message 510 in FIG. 5).By virtue of the above operation, the telephone controller 164 requeststhe telephone 162 to originate a call to telephone 163 (501). Thetelephone 162 originates the call and the incoming call arrives at thetelephone 163 (502). When the call arrives, the telephone 163 sonotifies the telephone controller 165 (503). Upon being notified of theincoming call, the telephone controller 165 requests that anincoming-call response be sent to the telephone 162, thereby completingthe connection (503 to 505).

[0125] 2. Phase A: Call Setup Phase

[0126] Phases from Phase A onward constitute a connection procedure thatbasically is the same as that of the prior art. This phase is aprocedure through which agreement is obtained for the purpose of settingup a call between the terminals A and B. The originating terminal (A)103 sends a call set-up response to the call-terminating terminal (B)102 by the Set-Up message 301, and the terminal B decides whether or notto set up the call. If the call is set up, the terminal 102 notifies theoriginating terminal 103 of call set-up by Connect message 302 andreports also the address (connect address) used in the ensuing Phase B.The details of the procedure of Phase A will now be described withreference to FIG. 4 on the basis of FIG. 1.

[0127] First, the connection controller 141 of the control unit 120 interminal A edits an IP packet in which has been placed a message (Set-Upmessage 301) requesting the set-up of a call the destination whereof isthe IP address of the IP interface 127 of controller 121 in the VoIPterminal B of the communicating party. The connection controller 141requests the IP interface 126 to transmit this IP packet. The IPinterface 126 transmits the IP packet in the direction of the IPinterface 127 via the IP network.

[0128] Upon receiving the call set-up request message from the terminal103 via the IP interface 127, the terminal 102 delivers this requestmessage to the connection controller 143 of the control unit 121. Theconnection controller 143 decides whether this call set-up request canbe answered and, if it can be answered, sends an answer message (Connectmessage 302) back to terminal A via the IP network. The contact address(IP address and port number) used in the ensuing Phase B is reported atthis time. In the example of FIG. 1, the Connect message 302 reports theIP address and port number necessary to communicate with the mediacontroller 144 that exercises control in Phase B.

[0129] Upon receiving the above-mentioned answer message, the connectioncontroller 141 of terminal 103 in effect agrees with terminal 103 toconnect the call and delivers the privilege for subsequent control tothe media controller 142 together with the IP address and port number(contact address) of the terminal 102 used in the ensuing Phase B (Start303).

[0130] 3. Phase B: Initial Communication and Capability Exchange

[0131] The media controller 142 of terminal 103 that obtained thecontrol privilege edits an IP packet having information necessary forvoice communication, the information including (1) informationindicating the voice encoding scheme of terminal A, (2) the IP addressof the IP interface 151 that sends and receives voice packets, and (3)the port number of the IP packetizing unit 150, and sends thisinformation (Open Logical Channel message 304) to the destinationindicated by the IP address and port number of terminal B that werereported through the procedure of Phase A. It should be noted that theIP address and port number of (1), (2) above constitute informationalready obtained from the IP packetizing unit 150 through the procedureof Phase S.

[0132] Upon receiving the Open Logical Channel message, the mediacontroller 144 of control unit 121 in terminal 102 determines whetherthe voice encoding scheme on the side of terminal B matches therequested encoding scheme. If the schemes match and voice communicationis possible, the terminal 102 edits an IP packet having informationnecessary for voice communication, the information including the IPaddress of the IP interface 129 that sends and receives voice packets,and a port number for selecting the voice IP packetizing unit 125, andsends this IP packet to the terminal 10 e (Open Logical Channel Ack306). As a result of these operations, information for communicatingvoice between both VoIP terminals A and B is obtained on both sides.

[0133] The foregoing is an example in which the H.323 protocol is used.However, a connection can be established using SIP (Session InitiationProtocol) instead of this protocol. In such case the sequence becomes asshown in FIG. 6 by way of example. In this sequence, Phases A and B areconsolidated and expressed by a single message. Specifically, theconnection controller 141 of terminal 103 queries the media controller142 regarding the conditions usable in media communication (401) and, asa result, information necessary for media communication, namely (1) thevoice encoding scheme of terminal A, (2) the IP address of the IPinterface 151 and (3) port number of the IP packetizing unit 150, etc.,is obtained. Next, the connection controller 141 sends the a connectionset-up request message, which is inclusive of this information, to theconnection controller 143 of terminal B (Invite message 402) via the IPnetwork. Upon receiving the Invite message 402, the media controller 142of terminal B determines whether the connection can be established and,if the connection can be established, reports the voice communicationconditions of terminal A to the media controller 144 of terminal B,acquires the voice communication conditions (403) on the side ofterminal B from the media controller 144 and sends this information tothe connection controller 141 of terminal A by OK message 404. In orderto verify receipt of the OK message, the connection controller 141 ofterminal A transmits the ACK message 416 to terminal B.

[0134] The connection controller 141 of terminal A delivers theinformation of the OK message to the media controller 142. As a resultof the procedure set forth above, information for communicating mediabetween the VoIP terminals A and B is obtained on both sides.

[0135] 4. Phase C: Establishment of Audiovisual Communication

[0136] The media controllers 142, 144 of both VoIP terminals A and Bnotify the IP packetizing units 150, 125 of the destination IP addressesand port numbers, which are for sending and receiving voice packets,acquired through the above-described procedure, and the IP packetizingunit 150 starts sending the voice signal using the reported IP addressand port number as the destination. Start messages (305, 333) in FIG. 4and Start messages (407, 434) in FIG. 6 correspond to these parts of theprocedure. In this case, the media controller 142 transmits the Startmessages (333 and 434) to the IP packetizing unit 150 via the IPnetwork. That is, the Start messages 333, 434 are sent to IP address ofthe IP interface 151 and port number of the IP packetizing unit 150 thatwere obtained by the procedure of Phase S.

[0137] The voice signal received from the voice/signal converter via thevoice signal transmitting unit is packetized by the IP packetizing unit150, arrives at the IP interface 129 of terminal B having the IP addressof the destination and is input to the receiving-side IP packetizingunit 125 selected by the specified port number. The IP packetizing unit125 converts the entered voice packet to a voice signal and inputs thevoice signal to the voice/signal converter 123. The latter converts thevoice signal to voice and outputs the same. The voice signal in theopposite direction is transmitted in a similar manner, whereby voicecommunication becomes possible (voice packets are sent and received at308 and 309).

[0138] 5. Phase D: Call Service

[0139] By changing the IP address of the communicating party to anotherIP address during communication, it is possible with the voicecommunication established in Phase B to change the destination of theconnection. Services such as third-party conversation and call transferare implemented using this function.

[0140] 6. Phase E: Call Termination

[0141] In order to release a connected call, the connection controller141 of the terminal 103 sends a release request message Release or Bye(309 in FIG. 4 and 410 in FIG. 6) to the terminal 102 on the called sideand instructs the IP packetizing unit 150 to stop the sending of voice(Stop 313, 334 in FIG. 4 and Stop 414, 435 in FIG. 6). Upon receivingthe release request message, the terminal 102 at the communicationdestination instructs the IP packetizing unit 125 on the side of thisterminal to halt the sending of voice (Stop 311, 312 in FIG. 4 and Stop412, 413 in FIG. 6) and sends a message to answer the release request(Release Ack or OK message) (310 in FIG. 4 and 411 in FIG. 6). As aresult, the resources that were being used in the connection of the callare released and the call can be disconnected. If the connectioncontroller 141 of terminal 103 that requested release cannot receiveRelease Ack 310 within a fixed period of time, this terminal resends therelease request message. This makes it possible to release the callconnection reliably even in cases where the message has been lost. Afterthe call is released, the media signal transmitting unit connected inPhase S is released. This is carried out by sending a disconnect requestmessage from the control unit of terminal 103 to the telephonecontrollers 164, 165. In a case where the control unit of terminal Acontinues with the connection of another call, the procedure from PhaseA onward is executed without effecting release, thereby making itpossible to connect the other call.

[0142] A case in which terminal 103 originates a call has beendescribed. The procedure when an incoming call arrives at terminal 103from terminal 102 is executed in similar fashion; the sequence diagramsare illustrated in FIGS. 7 and 8. However, FIG. 7 shows the connectionsequence for a VoIP call at the time of an incoming call in the case ofthe H.323 protocol and FIG. 8 the connection sequence for a VoIP call atthe time of an incoming call in the case of SIP.

[0143] In the first embodiment, there is no limitation regarding aspecific network used as the public telephone network. However, athird-generation mobile network currently under consideration can beapplied as the network on the side of terminal A. Such a mobile networkhas both an IP communication function and a voice communication functionand can be implemented in an efficient manner.

[0144] (C) Second Embodiment

[0145] According to a second embodiment of the present invention, amedia gateway serving as an IP packetizing unit is placed in a publictelephone network and voice is transmitted up to the media gatewaywithout being packetized using an existing network. The overallconstruction of this embodiment is the same as that of the firstembodiment shown in FIG. 1.

[0146] (a) Construction of Media Signal Transmitting Unit

[0147]FIG. 9 is a block diagram illustrating the second embodiment, inwhich the media gateway is placed in the public telephone network as theIP packetizing unit. Components in FIG. 9 identical with those of thefirst embodiment shown in FIG. 2 are designated by like referencecharacters. The voice signal transmitting unit 160, which exemplifiesmedia signal transmitting means, includes the telephone switch 170constituting a public telephone network; the telephone 163, which isconnected to the switch 170; the telephone controller 165 forcontrolling the telephone 163; some of the functions of the mediagateway (MG) 171, which is connected to the switch 170; and the mediagateway controller (MGC) 172.

[0148] The media gateway 171 has both a function for interfacing thepublic telephone network and a function for interfacing an IP network.More specifically, the media gateway 171 has a plurality of linesconnected to the telephone switch 170 and receives a voice signal fromthe telephone switch 170 via a line specified by the media gatewaycontroller 172. The media gateway 171 packetizes this voice signal,transmits the voice IP packet in the direction of the destinationterminal 102, converts a voice IP packet, which has been acquired fromthe IP network 130, to a voice signal and sends this voice signal to theside of terminal 103 via this line.

[0149] The media gateway controller 172 controls the media gateway 171in accordance with a predetermined protocol (the Megaco protocol, whichis a protocol compliant with ITU-T Recommendation H.248), and controlsconnection by exchanging call control signals with the public telephonenetwork by a predetermined signaling system, e.g., Common ChannelSignaling System No. 7. For example, if the telephone number oftelephone 163 and the line number of media gateway 171 are specified bya call control signal from the media gateway controller 172 to requestthe telephone switch 170 for a connection, the telephone switch 170connects the telephone 163 with the media gateway 171.

[0150] The control unit 120 of terminal 103 is capable of communicatingwith the media gateway controller 172 via the IP network 130. As will beset forth in the connection sequence described below, the telephone 163in the voice signal transmitting unit 160 and the media gateway 171 areconnected by an exchange of control signals between the media gatewaycontroller 172 and control unit 120. Further, in a manner to the firstembodiment, the control unit 120 of terminal 103 is connected directlyto the telephone controller 165 so that it can control the telephone163. The voice/signal converter 122 is connected to the telephone 163and can send and receive voice signals to and from the media gateway 171via the telephone switch 170.

[0151] (b) Connection Sequence

[0152] In the second embodiment, the construction of the voice signaltransmitting unit 160 differs from that of the first embodiment and,hence, the corresponding portion of the connection sequence alsodiffers. FIG. 10 illustrates the VoIP call connection sequence accordingto the second embodiment, and FIG. 11 shows a connection sequence forconnecting the voice/signal converter 122 and the media gateway 171.

[0153] 1. Phase S: Media Connection Setup

[0154] As in the first embodiment, the connection controller 141 ordersthe media controller 142 to make preparations for media communicationbefore a call is established (Preparation 330).

[0155] Upon being so ordered, the media controller 142 requests themedia gateway 171 via the IP network and media gateway controller 172 toconvert the voice signal to an IP packet (Request 331). In response tothis request, the media gateway 171 sends back, to the media gatewaycontroller 172, the necessary information such as the IP address andport number of the packetizing unit that performs the IP packetizing,and the encoding scheme used when the voice signal is IP-packetized. Themedia gateway controller 172 reports this information to the mediacontroller 142 via the IP network (Response 332)

[0156] Next, the media controller 142 controls the voice signaltransmitting unit 160 to connect the voice/signal converter 122 and themedia gateway 171 (341).

[0157] More specifically, as shown in FIG. 11, the media controller 142notifies the media gateway controller 172 of the telephone number of thetelephone 163 connected to the voice/signal converter 122 and requeststhat a call be originated to this number (Connect Req. 341). Further,the media controller 142 requests the telephone controller 165 oftelephone 163 on the side of the voice/signal converter to answer ifthere is an incoming call (answer preparation message 510). If anorigination request is issued, the media gateway controller 172 requeststhe telephone switch 170 to connect the media gateway 171 to thespecified telephone 163 via a predetermined line by a call controlsignal (501). As a result, an incoming call arrives at the telephone 163via the public telephone network (502, 503). When the incoming callarrives, the telephone controller 165 responds by completing theconnection (504). An answer signal is sent from the telephone switch 170to the media gateway controller 172 (505, 506). Upon receiving theanswer signal, the media gateway controller 172 notifies the mediagateway 171 of completion of the connection to the public telephonenetwork and completes the connection. The media gateway controller 172thenceforth sends the media controller 142 a Connect Complete message342 indicative of completion of the connection.

[0158] 2. Phase A: Call Setup Phase

[0159] Phase A is exactly the same as Phase A of the first embodimentand need not be described again.

[0160] 3. Phase B: Initial Communication and Capability Exchange

[0161] Phase B is exactly the same as Phase B of the first embodimentand need not be described again.

[0162] 4. Phase C: Establishment of Audiovisual Communication

[0163] The media controllers 142, 144 of both VoIP terminals A and Bnotify the IP packetizing unit (media gateway MG) 171 and the IPpacketizing unit 125, respectively, of the destination IP addresses andport numbers, which are indicative of the destination to which the voicepacket is to be transmitted, acquired through the above-describedprocedure, and the IP packetizing units 171, 125 start sending the voiceIP packet using the reported IP address and port number as thedestination. Start messages (305, 333) in FIG. 10 correspond to theseparts of the procedure. In this case, the media controller 142 transmitsthe Start message 333 to the media gateway controller 172, whichcontrols the media gateway 171, via the IP network. In response, themedia gateway controller 172 sets the IP address and port number ofterminal B in the media gateway 171 to thereby make voice communicationpossible.

[0164] A voice IP packet sent from the media gateway 171 arrives at theIP interface 129 (FIG. 1), which has the set IP address of thecommunicating terminal, via the IP network 130. The voice IP packetenters the IP packetizing unit 125 having the specified port number andis converted to a voice signal by the IP packetizing unit 125. Thevoice/signal converter 123 converts the voice signal to voice andoutputs the same. The voice signal in the opposite direction istransmitted in a similar manner, whereby voice communication becomespossible (voice packets are sent and received at 308).

[0165] 5. Phase D: Call Service

[0166] By changing the IP address of the communicating party to anotherIP address during communication in response to a request issued to themedia gateway controller 172, it is possible with the voicecommunication established in Phase B to change the destination of theconnection. Services such as third-party conversation and call transferare implemented using this function.

[0167] 6. Phase E: Call Termination

[0168] In order to release a connected call, the connection controller141 of the terminal 103 sends the release request message Release (309)and instructs the media gateway 171 to stop the sending of voice (313,314). Upon receiving the release request message, the connectioncontroller 143 of terminal B at the destination instructs the IPpacketizing unit 125 to halt the sending of voice (311, 312) and sendsthe connection controller 141 of terminal A the message Release Ack toanswer the release request (310). As a result, the resources that werebeing used in the connection of the call are released and the call canbe disconnected. If the terminal 102 that requested release cannotreceive Release Ack 310 within a fixed period of time, this terminalresends the release request message. This makes it possible to releasethe call connection reliably even in cases where the message has beenlost. After the call is released, the media signal transmitting unitconnected in Phase S is released. This is carried out by sending adisconnect request message from the control unit of terminal 103 to themedia gateway 171 and telephone controller 165. In a case where thecontrol unit of terminal A continues with the connection of anothercall, the procedure from Phase A onward is executed without effectingrelease, thereby making it possible to connect the other call.

[0169] As mentioned above, the Megaco protocol (H.248 protocol) has beendefined as means by which the media gateway controller 172 controls themedia gateway 171. In accordance with this protocol, it is possible (1)to specify the IP address and port number of the party that iscommunicating with the media gateway 171, (2) to acquire the IP addressand port number used by the media gateway 171, to set up a lineconnected to the switch, and (4) to IP-packetize a voice signal receivedfor the line that has been set up.

[0170] (c) Modification of Second Embodiment

[0171]FIG. 12 is a block diagram illustrating a modification of thesecond embodiment. Components in FIG. 12 identical with those of thesecond embodiment shown in FIG. 9 are designated by like referencecharacters.

[0172] As mentioned above, the Megaco protocol is a protocol as means bywhich the media gateway controller 172 controls the media gateway 171.Accordingly, as shown in FIG. 12, the media controller 142 of terminal Ais provided with an MGC control function 142′ and the elements from thetelephone 163 on the side of terminal A to the media gateway (MG) 171are regarded as one virtual media gateway 200. If this arrangement isadopted, the media controller 142 can control the virtual media gateway200 as a higher order MGC by the Megaco protocol.

[0173] By virtue of this arrangement, the control unit 120 of terminal103 need not use a new protocol and can exercise control using thealready defined H.248 protocol (Megaco protocol).

[0174] (D) Third Embodiment

[0175]FIG. 13A is a block diagram illustrating a media communicationsystem according to a third embodiment in which the IP packetizing meansis placed in a RAN (Radio Access Network). Components in FIG. 13Aidentical with those of the first embodiment shown in FIG. 1 aredesignated by like reference characters. This embodiment differs in thata mobile communication network is used as the network that accesses theIP network 130, and in that a mobile terminal is used as the terminal A.More specifically, the media communication system of the thirdembodiment has a mobile communication network 180 as the network foraccessing the IP network 130, has a mobile terminal 104 as the terminalA, and has wireless means for mobile communication as means fortransmitting voice signals. The wireless means for mobile communicationis constituted by a base-station facility or the like including a radiotransceiver, which is for modulating and demodulating radio signals fromthe mobile terminal 104, and a radio base station 181. The mediacommunication system according to the third embodiment has the IPpacketizing unit 150 placed in the mobile communication network 180. TheIP packetizing unit 150 is connected to the radio base station 181 toexchange voice signals with the voice/signal converter 122 of the mobileterminal 104, and is connected to the IP network 130 via the IPinterface 151 to exchange IP packets. An SGSN/GGSN 182 having a gatewayfunction for a 3GPP core network is disposed between the radio basestation 181 and the IP network 130.

[0176] Communication of control signals for connecting ordinarytelephone calls and data calls is performed between the mobile terminal104 and radio base station 181 (IP packetizing unit 150). The mobileterminal 104 and the IP packetizing unit 150 use these control signalcommunication means to communicate with each other and exchange controlinformation through a sequence similar to these of the first and secondembodiments. In this case, the radio base station 181 is capable ofconnecting the voice/signal converter 122 and IP packetizing unit 150 bya voice channel in the same manner as that of an ordinary voice call. Bytransmitting a control signal from the control unit 120 of mobileterminal 104 to the radio base station 181 (IP packetizing unit 150),the connection can be changed over freely. This makes it possible toraise the degree of freedom of connections.

[0177] In the case described above, a control signal from the mobilestation is sent to the IP packetizing unit 150 via the radio basestation 181. However, it can also be so arranged that a control signalis sent to the IP packetizing unit 150 via the IP network.

[0178] Further, if the IP network is classified as an asynchronouscommunication network and the mobile network as a synchronouscommunication network, then the signal conversion apparatus 155 will beprovided in the base-station facility and connected to the asynchronousIP network 130, as depicted in FIG. 13B. The signal conversion apparatus155 comprises: (1) first conversion means 150 a for converting asynchronous voice signal, which the radio base station 181 has receivedfrom the mobile terminal 104 via a radio channel, to an asynchronousvoice signal of a destination; (2) sending means (IP interface) 151 forsending the asynchronous voice signal obtained by the conversion to theasynchronous communication network 130; (3) second conversion means 150b for receiving an asynchronous voice signal from the asynchronouscommunication network 130 and converting this signal to a synchronousvoice signal; and (4) a transceiver unit 150 c for transmitting thesynchronous voice signal obtained by the conversion to the radio basestation 181 in such a manner that this signal will be transmitted to themobile station 104 via the radio channel.

[0179] Modification

[0180] As shown in FIG. 13C, the media gateway (MG) 171 is provided asthe IP packetizing unit 150 and IP interface 151, and the media gatewaycontroller (MGC) is provided as the control means of the media gateway171. The voice connection from the mobile terminal 104 to the mediagateway MG is established via the radio base station 181, and control ofthe media gateway MG is exercised by the media gateway controller MGC inaccordance with a command from the mobile terminal 104.

[0181] If the mobile terminal 104 is provided with the MGC controlfunction in this case, the elements from the voice/signal converter 122of the mobile terminal to the media gateway MG disposed in the mobilenetwork can be regarded as one virtual gateway. If this arrangement isadopted, the mobile terminal 104 can control the virtual media gatewayMG utilizing a protocol (Megaco protocol) the same as that which themedia gateway controller MGC uses to control the media gateway MG.

[0182] (E) Fourth Embodiment

[0183]FIG. 14 is a block diagram illustrating a fourth embodiment inwhich a private VoIP network is accessed from the outside. Components inFIG. 14 identical with those of the first embodiment shown in FIG. 1 aredesignated by like reference characters.

[0184] This is a communication system in which a closed private IP mediacommunication network (private VoIP network) 190 is constructed in acorporation or business and is connected to the external public IPnetwork 130 via a firewall 191. In this communication system, thecontrol unit 120 of the external terminal 103 is capable of VoIPcommunication with the terminal 102 of the intracorporate IP network 190via the public IP network 130 and firewall 191. Often, however,transmitting a VoIP voice packet through a public IP network andfirewall is not realistic because of problems relating to IPcommunication speed and firewall speed.

[0185] According to the fourth embodiment, this communication system isadapted in such a manner that the external terminal 103 can communicatemedia with the internal terminal 102 directly via the intracorporate IPnetwork 190 without the intervention of the firewall 191. To achievethis, the IP packetizing unit 150 is connected to the private VoIPnetwork (intracorporate IP network) 190 via the IP interface 151, the IPpacketizing unit 150 and the voice/signal converter 122 of the externalterminal 103 are connected by the voice signal transmitting unit 160,and voice signals can be sent and received in both directions. Anordinary public telephone network can be used as means for implementingthe voice signal transmitting unit 160, as in the first embodiment ofFIG. 2, and the connection sequence is the same as that of the firstembodiment. A mobile communication network can also be used as alternatemeans for implementing the voice signal transmitting unit 160, as in thethird embodiment of FIG. 13A.

[0186] The control unit 120 of the external terminal 103 performscontrol via the IP network 130, firewall 191 and intracorporate IPnetwork 190 in such a manner that the IP packetizing unit 150 operatesas its own IP packetizing unit when a call is generated, and connectsthe voice signal transmitting unit 160 in such a manner that theinternal voice/signal converter 122 and IP packetizing unit 150 areconnected. Upon completion of connection control, the control unit 120of external terminal 103 sends and receives voice signals to and fromthe internal terminal 102 via the voice/signal converter 122, voicesignal transmitting unit 160, IP packetizing unit 150 and intracorporateIP network 190.

[0187] As a result, the external terminal 103 can send voice signalsusing the intracorporate IP network 190 just as if it were connecteddirectly to the intracorporate IP network 190, without the interventionof the firewall 191.

[0188] (F) Fifth Embodiment

[0189]FIG. 15 is a block diagram illustrating a fifth embodiment inwhich the firewall is bypassed.

[0190] In this communication system in which the intracorporate IPnetwork (intranet) 196 is connected to the public IP network 130 via thefirewall 195, the VoIP terminal 101, which is connected to theintracorporate IP network 196, is capable of VoIP communication with theVoIP terminal 102 via the intracorporate IP network 196, firewall 195and IP network 130.

[0191] In general, when the intracorporate IP network 196 and public IPnetwork 130 are connected, the connection is made through the firewall195 in order to assure security, all IP packets are checked at thefirewall to determine whether or not they should pass, and security issafeguarded in such a manner that inappropriate IP communication willnot take place. With VoIP communication, however, 10 to 50 IP packetsare transferred in one second. Transfer of a large number of IP packetsleads to a greater amount of processing at the firewall and considerablefirewall resources are consumed in order to execute this processing.Voice IP packets in VoIP communication, on the other hand, contain onlyvoice information and it is therefore unnecessary to subject each andevery voice IP packet to stringent scrutiny to determine whether thepacket should pass or not.

[0192] According to the fifth embodiment, therefore, IP-packet relaymeans 197 is provided in parallel with the firewall 195 and a voice IPpacket is communicated via the IP-packet relay means 197 afterconnection negotiation control is performed between the terminals 101and 102. If this expedient is adopted, it can be so arranged that thevoice IP packet will not traverse the firewall 195. This makes itpossible to reduce the amount of processing at the firewall.

[0193] When a call is generated, the VoIP terminal 101 communicates withthe IP-packet relay means 197 via the intracorporate IP network 196firewall 195 and public IP network 130 and performs control in such amanner that the IP-packet relay means 197 operates as its own IP-packetrelay means. Further, the terminal 101 controls connection in such amanner that the voice/signal converter 122 can send a voice signal tothe terminal 102 via the intracorporate IP network 196, IP-packet relaymeans 197 and public IP network 130. Upon completion of the connection,the voice signal output from the voice/signal converter 122 isIP-packetized by the IP packetizing unit 124 and sends the packet to theVoIP terminal 102 via the intracorporate IP network 196, IP-packet relaymeans 197 and public IP network 130.

[0194] Though the media signal is described as being a voice signal, thepresent invention is not limited to a voice signal and can be applied tosignals such as an image signal and signal that is a combination ofvoice and images.

[0195] Thus, in accordance with the present invention, terminals can beconnected via an IP network to communicate the media signal even if themedia signal is not IP-packetized completely overall segments of thecommunication path between the terminals.

[0196] Further, in accordance with the present invention, theIP-packetizing of voice is not performed in a terminal but in anapparatus disposed in close proximity to the IP network. This makes itpossible to perform VoIP communication with little decline in voicequality. Moreover, it is possible to carry out end-to-end control, whichis one of the merits of VoIP communication, thereby enabling theprovision of flexible service.

[0197] Further, in accordance with the present invention, even if thereis a segment of the communication path that does not have sufficientdata transmission bandwidth, e.g., a wireless segment, voice istransmitted over this segment as is without being converted to a voiceIP packet. As a result, delay of IP packets can be reduced and a declinein voice quality can be avoided. In addition, since delay of IP packetscan be reduced, the size of overhead in the header of an IP packet doesnot present a problem and it is possible to dispense with a highlysophisticated header compression function.

[0198] Further, in accordance with the present invention, it is possibleto provide a terminal apparatus and a signal conversion apparatus thatare capable of communicating media.

[0199] Further, in accordance with the present invention, voice istransmitted as is using a public network or mobile network withoutrelying upon IP packetizing over segments that do not possess sufficientdata transmission bandwidth. As a result, facilities such as an existingvoice telephone network can be utilized effectively. This is extremelyadvantageous to communication companies and users.

[0200] Further, in accordance with the present invention, a terminal canbe provided with an interface exactly the same as that of theconventional VoIP terminal. As a result, the terminal on the side of thecommunicating party can set up calls and provide service throughhandling that is exactly the same without distinguishing between theterminal of the invention and a VoIP terminal of the prior art.

[0201] Further, in accordance with the present invention, it is possiblefor a business equipped with a private VoIP network having a VoIP-basedextension to communicate just as if a connection has been made directlyto the extension from the outside using an existing telephone network.This makes possible the implementation of highly effective means for useas intracorporate communication means.

[0202] Further, in accordance with the present invention, it is possibleto dispense with processing for verifying voice IP packets at thefirewall. This makes it possible to reduce the amount of firewallprocessing, to dispense with the need to provide the firewall withsophisticated functionality and to hold down cost.

[0203] As many apparently widely different embodiments of the presentinvention can be made without departing from the concept and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A media communication system for performing mediacommunication between first and second terminals, each of which isconstructed so as to be capable of IP communication, via an IP network,comprising: an IP packetizing unit for IP-packetizing and sending, tothe IP network, a media signal sent from the first terminal, and forconverting an IP packet received from the IP network to a media signaland sending the media signal to the first terminal; a media signaltransmitting unit for connecting a media/signal converter, which isprovided within the first terminal, to said IP packetizing unit, and fortransmitting a media signal and the first terminal having, in additionto said media/signal converter for generating a media signal andreceiving a media signal from the IP packetizing unit, a controller forcontrolling connection to the second terminal and for controllingsending/receiving of a media signal when a call is generated; whereinwhen a call is generated, the first terminal performs control in such amanner that said IP packetizing unit operates as its own IP packetizingunit, and controls said media signal transmitting unit to connect saidmedia/signal converter and said IP packetizing unit; and upon completionof the connection, the first terminal sends and receives media signalsto and from the second terminal via said media/signal converter, saidmedia signal transmitting unit, said IP packetizing unit and said IPnetwork
 2. The system according to claim 1, wherein when the controllerof said first terminal performs connection control, said controllercommunicates with said IP packetizing unit to acquire an IP address andport number of said IP packetizing unit, reports this IP address andport number to the second terminal and receives an IP address and portnumber of the second terminal from the second terminal and reports theseto said IP packetizing unit; said IP packetizing unit packetizes a mediasignal received from the media/signal converter via said media signaltransmitting unit and sends the resulting packet to the IP network usingthe IP address and port number of the second terminal as thedestination; and the second terminal sends a media-signal IP packet tothe IP network using the IP address and port number of said IPpacketizing unit as the destination.
 3. The system according to claim 1,wherein said media signal transmitting unit is constructed using apublic network.
 4. The system according to claim 1, wherein said mediasignal transmitting unit is constructed using a mobile communicationnetwork, and said mobile communication network is used as IPtransmission means to send and receive control signals between the firstterminal and said IP packetizing unit.
 5. The system according to claim3, wherein said media signal transmitting unit includes a telephone onthe side of the first terminal, a public telephone network and atelephone on the side of said IP packetizing unit; and when thecontroller of said first terminal performs connection control, saidcontroller calls the telephone on the side of the first terminal fromthe telephone on the side of the IP packetizing unit and connects saidmedia/signal converter and said IP packetizing unit.
 6. The systemaccording to claim 3, wherein said media signal transmitting unitincludes a telephone on the side of the first terminal, a publictelephone network and a telephone on the side of said IP packetizingunit; and when the controller of said first terminal performs connectioncontrol, said controller calls the telephone on the side of the IPpacketizing unit from the telephone on the side of the first terminaland connects said media/signal converter and said IP packetizing unit.7. The system according to claim 3, wherein said IP packetizing unit isdisposed within a public telephone network so as to be connectable to apublic network switch and so as to be capable of communicating with thefirst terminal via the IP network.
 8. The system according to claim 7,wherein said IP packetizing unit provided in the public network isconstituted by a media gateway and a media gateway controller isprovided for communicating with the controller of the first terminal viathe IP network to control said media gateway by a predeterminedprotocol.
 9. The system according to claim 8, wherein when thecontroller of said first terminal performs connection control, saidcontroller calls a telephone on the side of the first terminal from saidmedia gateway and connects said media/signal converter and said IPpacketizing unit.
 10. The system according to claim 8, wherein when thecontroller of said first terminal performs connection control, saidcontroller calls said media gateway from a telephone on the side of thefirst terminal and connects said media/signal converter and said IPpacketizing unit.
 11. The system according to claim 8, wherein thecontroller of said first terminal is provided with a function of saidmedia gateway controller, and said controller regards elements from atelephone on the side of the first terminal to said IP packetizing unitas one virtual media gateway and controls this virtual media gateway bysaid protocol.
 12. The system according to claim 2, wherein said mediasignal transmitting unit is constructed using a mobile communicationnetwork, said IP packetizing unit is provided within the mobilecommunication network and communication between the first terminal andsaid IP packetizing unit is implemented in accordance with awireless-access communication protocol.
 13. The system according toclaim 12, wherein said IP packetizing unit provided within said mobilecommunication network is constituted by a media gateway and a mediagateway controller is provided for communicating with the controller ofthe first terminal to control said media gateway by a predeterminedprotocol.
 14. The system according to claim 13, wherein the controllerof said first terminal is provided with a function of said media gatewaycontroller, and said controller regards said media gateway and saidmedia gateway controller as one virtual media gateway and controls thisvirtual media gateway by said protocol.
 15. A media communication systemfor performing media communication between first and second terminals,each of which is constructed so as to be capable of IP communication,via an IP network, comprising: a public IP network to which the firstterminal is connected; an intracorporate IP network to which the secondterminal is connected and which is capable of IP media communication byan extension; a firewall provided between said public IP network andsaid intracorporate IP network; an IP packetizing unit forIP-packetizing and sending, to said intracorporate IP network, a mediasignal sent from the first terminal, and for converting an IP packetreceived from said intracorporate IP network to a media signal; a mediasignal transmitting unit for connecting a media/signal converter, whichis provided within the first terminal, to said IP packetizing unit, andfor transmitting a media signal; and the first terminal having, inaddition to said media/signal converter for generating a media signaland receiving a media signal from the IP packetizing unit, a controllerfor controlling connection to the second terminal and for controllingsending/receiving of a media signal when a call is generated; whereinthe controller of said first terminal performs control via said publicIP network, said firewall and said intracorporate IP network in such amanner that said IP packetizing unit operates as its own IP packetizingunit, and controls said media signal transmitting unit to connect saidmedia/signal converter and said IP packetizing unit; and upon completionof the connection, the first terminal sends and receives media signalsto and from the second terminal via said media/signal converter, saidmedia signal transmitting unit, said IP packetizing unit and saidintracorporate IP network.
 16. The system according to claim 15, whereinsaid media signal transmitting unit is constructed using a mobilecommunication network, and said mobile communication network is used asIP transmission means to send and receive control signals between thefirst terminal and said IP packetizing unit.
 17. A media communicationsystem for performing media communication between first and secondterminals, each of which is constructed so as to be capable of IPcommunication, via an IP network, comprising: an intracorporate IPnetwork, which is closed within a corporation, to which the firstterminal is connected and which is capable of IP media communication; apublic IP network to which the second terminal is connected; a firewallprovided between said intracorporate IP network and said public IPnetwork; and IP-packet relay means provided between said intracorporateIP network and said public IP network for bypassing said firewall; thefirst terminal having: an IP packetizing unit for IP-packetizing a mediasignal and sending it to said intracorporate IP network, and forconverting an IP packet received from said intracorporate IP network toa media signal; and a controller for controlling connection to thesecond terminal and for controlling sending/receiving of a media signalwhen a call is generated; wherein when a call is generated, thecontroller of said first terminal performs control via saidintracorporate IP network, said firewall and said public IP network insuch a manner that said IP-packet relay means operates as its own relaymeans, and controls connection in such a manner that a media signal iscapable of being transmitted via said intracorporate IP network, saidIP-packet relay means and said public IP network; and upon completion ofconnection control, the controller sends and receives media signals toand from the second terminal via said intracorporate IP network, saidIP-packet relay means and said public IP network.
 18. A signalconversion apparatus provided in a base-station facility and connectedto an asynchronous communication network, comprising: receiving meansfor receiving a control signal from a mobile station via a base stationor asynchronous communication network; means for converting asynchronous voice signal, which the base station has received from themobile station via a radio channel, to an asynchronous voice signaldirected to a destination decided by the control signal; and sendingmeans for sending the asynchronous voice signal obtained by theconversion to the asynchronous communication network.
 19. A signalconversion apparatus provided in a base-station facility and connectedto an asynchronous communication network, comprising: receiving meansfor receiving a control signal from a mobile station via a base stationor asynchronous communication network; conversion means for receiving anasynchronous voice signal from a destination, which is specified by thecontrol signal, via the asynchronous communication network andconverting the asynchronous voice signal to a synchronous voice signal;and sending means for sending the synchronous voice signal obtained bythe conversion to the base station in such a manner that the basestation will transmit this signal to the mobile station via the radiochannel.
 20. A signal conversion apparatus provided in a base-stationfacility and connected to an asynchronous communication network,comprising: receiving means for receiving a control signal from a mobilstation via a base station or asynchronous communication network; firstconversion means for converting a synchronous voice signal, which a basestation has received from a mobile station via a radio channel, to anasynchronous voice signal directed to a destination that has been set;first sending means for sending the asynchronous voice signal obtainedby the conversion to the asynchronous communication network; secondconversion means for receiving an asynchronous voice signal from the setdestination via the asynchronous communication network and convertingthis signal to a synchronous voice signal; and second sending means forsending the synchronous voice signal obtained by the conversion to thebase station in such a manner that this signal will be transmitted tothe mobile station via the radio channel.
 21. A terminal apparatus in amedia communication system for sending and receiving media signalsbetween terminals via an IP packetizing unit for IP-packetizing a mediasignal and sending it to an IP network and for converting an IP packetreceived from the IP network to a media signal, a media signaltransmitting unit for transmitting a media signal between a terminal andthe IP packetizing unit, and the IP network, said terminal apparatuscomprising: a media/signal converter for generating a media signal andreceiving a media signal from said IP packetizing unit via said mediasignal transmitting unit; and a controller which, when a call isgenerated, is for performing control in such a manner that said IPpacketizing unit operates as its own IP packetizing unit and forcontrolling said media signal transmitting unit to connect saidmedia/signal converter and said IP packetizing unit.